Signal processing method in wireless communication system and relay node therefor

ABSTRACT

A method is described for operating a device in a wireless communication system. The device communicates with a base station using a subframe for the device only; detects, by the device, a problem with a connection between the device and the base station. The device starts a timer upon detecting the problem with the connection between the device and the base station. The device releases a restriction of using the subframe for the device only, if the timer expires. The problem with the connection between the device and the base station is associated with a radio link failure. The detection of a problem with the connection between the device and the base station comprises detecting consecutive out-of-sync indications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.14/298,600 filed on Jun. 6, 2014, which issued as U.S. Pat. No.9,148,900 on Sep. 29, 2015, which is a Continuation of U.S. applicationSer. No. 13/322,060 filed on Nov. 22, 2011, which issued as U.S. Pat.No. 8,780,698 on Jul. 15, 2014, which is a National Phase application ofPCT/KR2011/002260 filed on Apr. 1, 2011, which claims the benefit under35 U.S.C. §119(e) of U.S. Provisional Application No. 61/320,298 filedon Apr. 1, 2010. The contents of all of these applications are herebyincorporated by reference as fully set forth herein in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for processing signals in awireless communication system.

Description of the Related Art

As an example of a mobile communication system to which the presentinvention is applicable, a 3^(rd) Generation Partnership Project LongTerm Evolution (3GPP LTE) will be briefly described.

An LTE system is a mobile communication system evolved from a UniversalMobile Telecommunications System (UMTS) system and the standard thereofis established in the 3GPP. The schematic structure of the LTE system isshown in FIG. 1.

FIG. 1 is a diagram showing a network architecture of an LTE systemwhich is an example of a mobile communication system.

The structure of the LTE system may be roughly divided into an EvolvedUMTS Terrestrial Radio Access Network (E-UTRAN) and an Evolved PacketCore (EPC).

The E-UTRAN includes at least one eNB (Evolved Node B or base station).An interface between a UE and an eNB is referred to as a Uu interfaceand an interface between an eNB and another eNB is referred to as a X2interface.

The EPC includes a mobility management entity (MME) for performing acontrol plane function and a serving gateway (S-GW) for performing auser plane function. An interface between an eNB and an MME is referredto as an S1-MME interface and an interface between an eNB and an S-GW isreferred to as an S1-U interface. These interfaces may be collectivelyreferred to as an S1 interface.

In a radio Uu interface, a radio interface protocol is defined. Theradio interface protocol is horizontally divided into a physical layer,a data link layer and a network layer. The radio interface protocol isvertically divided into a user plane (U-plane) for transmitting userdata and a control plane (C-plane) for signaling a control signal.

The radio interface protocol may be divided into L1 (first layer)including a physical layer (PHY), L2 (second layer) including aMAC/RLC/PDCP layer, and L3 (third layer) including a RRC layer based onthe three lower layers of an open system interconnection (OSI) standardmodel which is well-known in the art of communication systems, as shownin FIGS. 2 and 3. A pair of radio interface protocols exist in a UE andan E-UTRAN to perform a data transmission function of a Uu interface.

SUMMARY OF THE INVENTION

An object of the present invention devised to solve the problem lies ina method for receiving control information in a wireless communicationsystem and an apparatus thereof.

Another object of the present invention devised to solve the problemlies in control of a relay node (RN) subframe if a problem occurs inconnection of a Un interface between a donor eNB (DeNB) and an RN in anLTE-A system, in which, when a problem occurs in the Un interface, theRN releases the RN subframe and operates as a general UE so as toprevent interference when recovering the Un interface and to prevent theUE from attempting data transmission.

The object of the present invention can be achieved by providing amethod for processing signals by a wireless node in a wirelesscommunication system, including configuring a specific subframe forcommunicating with a network node, starting a timer if a problem of aconnection with the network node is detected, and releasing theconfigured specific subframe if the timer expires.

The method may further include performing recovery of problem using thespecific subframe while the timer is running.

The method may further include performing a connection with the networknode using any subframe if the timer expires.

The method may further include transitioning to a radio resource control(RRC) idle state if the timer expires, and performing a cell selectionprocedure.

The connection problem may be radio link failure (RLF), and the networknode may be a Node B.

According to the embodiments of the present invention, when a problemoccurs in an Un interface, the Un interface is recovered using a relaynode (RN) subframe up to an appropriate point of time, such that a timerequired for solving the problem of the Un interface is optimized.

The effects of the present invention are not limited to theabove-described effects and other effects which are not described hereinwill become apparent to those skilled in the art from the followingdescription.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 is a network architecture of an LTE system which is an example ofa mobile communication system;

FIGS. 2 and 3 are diagrams showing the structure of a radio interfaceprotocol between a UE and an E-UTRAN in an LTE system;

FIG. 4 is a diagram showing the configuration of a relay node, a Uninterface, a relay backhaul link and a relay access link in a wirelesscommunication system;

FIG. 5 is a diagram showing an example of relay node resourcepartitioning;

FIG. 6 is a flowchart illustrating the flow of an operation of a relaynode when an out-of-sync problem occurs in a physical channel of a Uninterface;

FIG. 7 is a flowchart illustrating the flow of an operation of a relaynode when radio link failure occurs in a Un interface; and

FIG. 8 is a block diagram of a communication device according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The configuration, operation and other features of the present inventionwill be understood by the embodiments of the present invention describedwith reference to the accompanying drawings. The following embodimentsare examples of applying the technical features of the present inventionto a 3rd Generation Partnership Project (3GPP) system. FIGS. 2 and 3 arediagrams showing the structure of a radio interface protocol between aUE and an E-UTRAN in an LTE system. The layers of the radio interfaceprotocol of FIGS. 2 and 3 will now be described.

The physical layer (PHY), which is the first layer, provides aninformation transfer service to a higher layer using a physical channel.The PHY layer is connected to a Media Access Control (MAC) layer,located above the physical layer, through a transport channel. Data istransferred between the MAC layer and the PHY layer through thetransport channel. The transport channel is roughly divided into adedicated transport channel and a common transport channel, depending onwhether or not a channel is shared. Data transfer between different PHYlayers, specifically between the respective PHY layers of transmittingand receiving sides, is performed through the physical channel.

Various layers may be located in a second layer. The MAC layer serves tomap various logical channels to various transport channels. The MAClayer performs a logical channel multiplexing function for mappingseveral logical channels to one transport channel. The MAC layer isconnected to a Radio Link Control (RLC) layer, which is a higher layer,via a logical channel, and the logical channel may be roughly dividedinto a control channel for transmitting information about the controlplane and a traffic channel for transmitting information about the userplane, according to the type of transmitted information.

The RLC layer of the second layer segments and concatenates datareceived from a higher layer, thereby controlling a data size so as tobe suitable for a lower layer to transmit data via a radio interface.The RLC layer provides three modes, namely, a transparent mode (TM), anunacknowledged mode (UM) and an acknowledged Mode (AM) to supportvarious QoSs requested by each radio bearer (RB). Especially, forreliable data transmission, the AM RLC performs a retransmissionfunction using an automatic repeat request (ARQ) scheme.

A packet data convergence protocol (PDCP) layer located at the secondlayer is used to efficiently transmit IP packets, such as IPv4 or IPv6packets, in a radio interface with a relatively narrow bandwidth. Forthis purpose, the PDCP layer reduces the size of an IP packet headerwhich is relatively great in size and includes unnecessary controlinformation, namely, performs a function called header compression.Accordingly, only necessary information can be included in the headerpart of data for transmission, so as to increase a transmissionefficiency of a radio interface. In the LTE system, the PDCP layer alsoperforms a security function. The security function includes a cipheringfunction for preventing data monitoring from a third party, and anintegrity protection function for preventing third party datamanipulation.

A radio resource control (RRC) layer located at a lowest portion of thethird layer is defined in the control plane. The RRC layer handleslogical channels, transport channels and physical channels for theconfiguration, re-configuration and release of radio bearers. Here, aradio bearer (RB) denotes a logical path provided by the first andsecond layers of radio protocols for data transfer between the UE andthe UTRAN. Generally, configuration of the RB indicates a process ofregulating radio protocol layers and channel characteristics necessaryfor providing a specific service, and configuring specific parametersand operation methods. The RB is divided into a signaling RB (SRB) and adata RB (DRB). The SRB is used as a path through which an RRC message istransmitted in a C-plane, while the DRB is used as a path through whichuser data is transmitted in a U-plane.

Downlink transport channels for transmitting data from a network to a UEmay include a Broadcast Channel (BCH) for transmitting systeminformation and a downlink Shared Channel (SCH) for transmitting otheruser traffic or control messages. Traffic or control messages of adownlink multicast or broadcast service may be transmitted either via adownlink SCH, or via a separate downlink Multicast Channel (MCH).

In addition, uplink transport channels for transmitting data from a UEto a network may include a Random Access Channel (RACH) for transmittingan initial control message and an uplink Shared Channel (SCH) fortransmitting user traffic or control messages.

Logical channels, which are located above the transport channels and aremapped to the transport channels, include a Broadcast Control Channel(BCCH), a Paging Control Channel (PCCH), a Common Control Channel(CCCH), a Multicast Control Channel (MCCH) and a Multicast TrafficChannel (MTCH).

A physical channel includes several subframes on a time axis and severalsubcarriers on a frequency axis. Here, one subframe includes a pluralityof symbols on the time axis. One subframe includes a plurality ofresource blocks and one resource block includes a plurality of symbolsand a plurality of subcarriers. In addition, each subframe may usecertain subcarriers of certain symbols (e.g., a first symbol) of asubframe for a physical downlink control channel (PDCCH), that is, anL1/L2 control channel. The length of one subframe is 0.5 ms and atransmission time interval (TTI) which is a time unit for transmittingdata is 1 ms which corresponds to two subframes.

Hereinafter, radio link failure (RLF) will be described.

A UE may determine that RLF has occurred if the following problemsoccur.

(1) First, it may be determined that RLF has occurred due to a physicalchannel problem.

A UE may determine that an out-of-sync problem has occurred in aphysical channel if the quality of a reference signal (RS) periodicallyreceived from an eNB through the physical channel is equal to or lessthan a threshold. If a predetermined number (e.g., N310) of out-of-syncproblems occurs, the physical layer informs an RRC layer that theout-of-sync problems have occurred. The RRC layer which receives theout-of-sync message from the physical layer operates a timer T310 andwaits for the problem of the physical channel to be solved while thetimer T310 is operated. If the RRC layer receives a message indicatingthat a predetermined number (e.g., N310) of consecutive in-sync problemshas occurred from the physical layer while the timer T310 is operated,the RRC layer determines that the problem of the physical channel hasbeen solved and stops the timer T310. However, if the in-sync message isnot received before the timer T310 expires, the RRC determines that RLFhas occurred.

(2) It may be determined that RLF has occurred due to a MAC randomaccess problem.

A UE performs a procedure including a random access resource selectionstep, a random access preamble transmission step, a random accessresponse reception step and a contention resolution step when performinga random access procedure at the MAC layer. If such a random accessprocedure is not successfully performed, a next random access procedureis performed after a back-off time. However, if a predetermined number(e.g., preambleTransMax) of random access procedures is not successfullyperformed, the MAC layer informs the RRC layer that the random accessprocedure is not successfully performed and the RRC layer determinesthat RLF has occurred.

(3) It may be determined that RLF has occurred due to a maximum RLCretransmission problem.

A UE retransmits an RLC PDU which is not successfully transmitted if anAM RLC layer of an RLC layer is used. Although the AM RLC layerretransmits a specific AMD PDU a predetermined number of times (e.g.,maxRetxThreshold), if transmission is not successfully performed, the AMRLC layer informs the RRC layer that transmission is not successfullyperformed and the RRC layer determines that RLF has occurred.

The RRC layer determines that RLF has occurred when the above threeproblems occur. If RLF has occurred, an RRC connection re-establishmentprocedure for re-establishing RRC connection with an eNB is performed.

An RRC connection re-establishment procedure which is performed when RLFoccurs is as follows.

If it is determined that a serious problem occurs in RRC connection, aUE performs an RRC connection re-establishment procedure in order tore-establish connection with an eNB. Serious problems which occur in RRCconnection include the following five problems, that is, (1) radio linkfailure (RLF), (2) handover failure, (3) mobility from E-UTRA, (4) PDCPintegrity check failure, (5) RRC connection reconfiguration failure.

If one of the above problems occurs, the UE operates a timer T311 andstarts an RRC connection re-establishment procedure. During thisprocess, the UE performs a cell selection procedure and a random accessprocedure and then accesses a new cell.

If an appropriate cell is detected through the cell selection procedurewhile the timer T311 is running, the UE stops the timer T311 and startsthe random access procedure. However, if an appropriate cell is notdetected before the timer T311 expires, the UE determines that RRCconnection failure has occurred and enters to an RRC_IDLE mode.

FIG. 4 is a diagram showing the configuration of a relay node, a Uninterface, a relay backhaul link and a relay access link in a wirelesscommunication system.

Relay technology relays data between a UE and an eNB. In an LTE system,if a UE is located a considerable distance from an eNB, communication isnot smoothly performed. In order to solve this problem, relay technologywas introduced in an LTE-A system. By using relay technology in a celledge region in which a channel state of an eNB is inferior, a high-speeddata channel can be provided and a cell service region can be extended.

In order to achieve such relay technology, a new network node called arelay node (RN) was introduced between a UE and an eNB. An eNB formanaging the RN is referred to as a donor eNB (DeNB). A newly generatedinterface between the RN and the DeNB is defined as a Un interface andis different from a Uu interface between a UE and a network node. FIG. 4shows the concept of the RN and the Un interface.

Instead of the DeNB, the RN serves to manage the UE. That is, the UEregards the RN as the DeNB. Thus, in the Uu interface between the UE andthe RN, MAC/RLC/PDCP/RRC which is Uu interface protocol used in theconventional LTE system is used without change.

The DeNB regards the RN as the UE or the eNB according to situation.That is, when the RN firsts accesses the DeNB, since the DeNB is notaware of presence of the RN, the RN accesses the DeNB through the randomaccess procedure as in the UE. After the RN accesses the DeNB, the RNoperates like an eNB which manages the UE connected thereto.Accordingly, the Un interface protocol not only has a Uu interfaceprotocol but also a network protocol function.

While the conventional RN technology was limited to the function of arepeater for amplifying and transmitting a signal, recently, RNtechnology has been developed into a more intelligent form oftechnology. Further, the RN technology is necessary to reduce costsrequired for installing more eNBs and costs required for maintaining abackhaul network in a next-generation mobile communication system,enlarge a service coverage and improve data throughput. As RN technologyhas been increasingly developed, an RN used in the conventional wirelesscommunication system needs to be supported in a new wirelesscommunication system.

As a function for forwarding link connection between an eNB and a UE toan RN has been introduced in a 3^(rd) Generation Partnership ProjectLong Term Evolution-Advanced (3GPP LTE-A) system, two links havingdifferent attributes are applied to uplink and downlink carrierfrequency bands. A connection link set between the eNB and the RN isreferred to as a backhaul link, Frequency Division Duplex (FDD) or TimeDivision Duplex (TDD) transmission using downlink resources is referredto as a backhaul downlink, and FDD or TDD transmission using uplinkresources is referred to as a backhaul uplink.

Referring to FIG. 4, as an RN is introduced in order to forward linkconnection between an eNB and a UE, two links having differentattributes are applied to uplink and downlink carrier frequency bands. Aconnection link set between the eNB and the RN is referred to as a relaybackhaul link. A backhaul link for performing transmission usingdownlink frequency bands (in case of FDD) or downlink subframes (in caseof TDD) as resources is referred to as a backhaul downlink and abackhaul link for performing transmission using uplink frequency bands(in case of FDD) or uplink subframes (in case of TDD) as resources isreferred to as a backhaul uplink.

A connection link set between an RN and a series of UEs is referred toas a relay access link. A relay access link for performing transmissionusing downlink frequency bands (in case of FDD) or downlink subframes(in case of TDD) as resources is referred to as an access downlink and arelay access link for performing transmission using uplink frequencybands (in case of FDD) or uplink subframes (in case of TDD) as resourcesis referred to as an access uplink.

The RN may receive information from the eNB through the relay backhauldownlink and transmit information to the eNB through the relay backhauluplink. The RN may transmit information to the UE through the relayaccess downlink and receive information from the UE through the relayaccess uplink.

In association with the use of the band (or the spectrum) of the RN, thecase where the backhaul link operates in the same frequency band as theaccess link is referred to as “in-band” and the case where the backhaullink and the access link operate in different frequency bands isreferred to as “out-band”. A UE (hereinafter, referred to as a legacyUE) which operates according to the existing LTE system (e.g.,Release-8) must access a DeNB both in in-band and out-band.

The RN may be classified into a transparent RN or a non-transparent RNdepending on whether or not the UE recognizes the RN. The term“transparent” indicates that the UE does not recognize whethercommunication with a network is performed through the RN and the term“non-transparent” indicates that the UE recognizes whether communicationwith a network is performed through the RN.

In association with control of the RN, the RN may be divided into a RNconfigured as a part of a DeNB and an RN for controlling a cell.

The RN configured as a part of the DeNB has a RN ID, but does not have acell identity. If at least a part of radio resource management (RRM) iscontrolled by an eNB belonging to a DeNB, (although the remaining partof the RRM is located at the RN), the RN is configured as a part of theDeNB. Preferably, such an RN may support a legacy UE. For example,examples of such an RN include various RNs such as smart repeaters,decode-and-forward relays or L2 (second layer) RNs and type-2 RNs.

The RN for controlling the cell controls one or several cells, providesa unique physical layer cell identity to each cell controlled by the RN,and uses the same RRM mechanism. From the viewpoint of the UE, there isno difference between accessing the cell controlled by the RN andaccessing the cell controlled by the general eNB. Preferably, the cellcontrolled by the RN may support a legacy UE. Examples of such an RNinclude a self-backhauling RN, an L3 (third layer) RN, a type-1 RN and atype-1a RN.

The type-1 RN is an in-band RN for controlling a plurality of cells.From the viewpoint of the UE, the plurality of cells is regarded ascells distinguished from a DeNB. Each of the plurality of cells has aphysical cell ID (defined in LTE Release-8) and the RN may transmit asynchronization channel thereof, a reference signal, etc. The UE maydirectly receive scheduling information and HARQ feedback from the RNand transmit a control channel (a scheduling request (SR), a CQI,ACK/NACK, etc.) thereof to the RN in a single cell. Legacy UEs (a UEwhich operates according to the LTE Release-8 system) regard the type-1RN as a legacy eNB (a base station which operates according to the LTERelease-8 system), that is, has backward compatibility. UEs whichoperate according to the LTE-A system regard the type-1 RN as an eNBdifferent from the legacy eNB, thereby improving performance.

The type-1a RN has the same features as the type-1 RN except that the RNoperates as an out-band RN. The operation of the type-1a RN may beconfigured such that influence on the operation of L1 (first layer) isminimized or eliminated.

The type-2 RN is an in-band RN which does not have a separate physicalcell ID and thus does not form a new cell. The type-2 RN is transparentto a legacy UE and a legacy UE recognizes presence of the type-2 RN. Thetype-2 RN may transmit a PDSCH, but may not transmit at least a CRS anda PDCCH.

In order to enable an RN to operate as an in-band RN, sometime-frequency resources must be reserved for a backhaul link and may beset so as not to be used for an access link. This is referred to asresource partitioning.

The general principle of resource partitioning in the RN will now bedescribed. A backhaul downlink and an access downlink may be multiplexedon one carrier frequency using a time division multiplexing (TDM) method(that is, only one of the backhaul downlink or the access downlink isactivated at a specific time). Similarly, a backhaul uplink and anaccess uplink may be multiplexed on one carrier frequency using a TDMmethod (that is, only one of the backhaul uplink or the access uplink isactivated in a specific timeframe).

Multiplexing of a backhaul link in FDD indicates that backhaul downlinktransmission is performed in a downlink frequency band and backhaul linktransmission is performed in an uplink frequency band. Multiplexing of abackhaul link in TDD indicates that backhaul downlink transmission isperformed in a downlink subframe of an eNB and an RN and backhaul uplinktransmission is performed in an uplink subframe of an eNB and an RN.

In case of an in-band RN, for example, if reception of a backhauldownlink from an eNB and transmission of an access downlink to a UE in apredetermined frequency band are simultaneously performed, a signaltransmitted from a transmitter of the RN may be received by a receiverof the RN and thus signal interference or RF jamming may occur in an RFfront end of the RN. Similarly, if reception of an access uplink from aUE and transmission of a backhaul uplink to an eNB in a predeterminedfrequency band are simultaneously performed, signal interference mayoccur in an RF front end of the RN. Accordingly, it is difficult toperform simultaneous transmission/reception by the RN in one frequencyband unless a received signal and a transmitted signal are sufficientlyseparated (e.g., unless a transmission antenna and a reception antennaare sufficiently geographically separated (for example, the transmissionand reception antennas are respectively mounted on and below theground).

In order to solve a signal interference problem, an RN does not transmita signal to a UE while receiving a signal from a DeNB. That is, a gap isgenerated in transmission from the RN to the UE and no signal istransmitted from the RN to the UE (including a legacy UE) during thegap. Such a gap may be set to configure a multicast broadcast singlefrequency network (MBSFN) subframe.

FIG. 5 is a diagram showing an example of RN resource partitioning.

In FIG. 5, a first subframe on the left may be a general subframe inwhich a downlink (i.e., access downlink) control signal and data aretransmitted from an RN to a UE, and a second subframe on the right maybe an MBSFN subframe in which a control signal is transmitted from an RNto a UE in a control region of a downlink subframe and no signal istransmitted from the RN to the UE in the remaining region of thedownlink subframe. In case of a legacy UE, since transmission of aphysical downlink control channel (PDCCH) is expected in all downlinksubframes (that is, since the RN needs to enable all legacy UEs withinthe coverage area thereof to receive the PDCCH so as to perform ameasurement function), the PDCCH needs to be transmitted in all downlinksubframes, for the accurate operation of the legacy UE.

Accordingly, even on a subframe (second subframe) set for downlink (thatis, backhaul downlink) transmission from an eNB to an RN, the RN doesnot receive a backhaul downlink, but transmits an access downlink in Nfirst (N=1, 2 or 3) OFDM symbols of the subframe. In contrast, since aPDCCH is transmitted from the RN to the UE in the control region of thesecond subframe, backward compatibility with a legacy UE served by theRN may be provided. In the remaining region of the second subframe, nosignal is transmitted from the RN to the UE and thus the RN may receivea signal from the eNB at this time. Accordingly, using such a resourcepartitioning method, the in-band RN does not simultaneously performaccess downlink transmission and backhaul downlink reception.

The second subframe will now be described in detail. The control regionof the second subframe may be referred to as an RN non-hearing interval.The RN non-hearing interval refers to an interval in which the RN doesnot receive a backhaul downlink signal and transmits an access downlinksignal. This interval may be set to 1, 2 or 3 OFDMs as described above.The RN may transmit an access downlink to the UE in the RN non-hearinginterval and receive a backhaul downlink from the eNB in the remainingregion. At this time, since the RN may not simultaneously performtransmission and reception in the same frequency band, it takesconsiderable time to switch the RN from a transmission mode to areception mode. Accordingly, a guard time (GT) needs to be set such thatthe RN is switched between the transmission mode and the reception modein a first part of a backhaul downlink reception region. Similarly, evenwhen the RN receives a backhaul downlink from the eNB and transmits anaccess downlink to the UE, a GT for switching the RN between thetransmission mode and the reception mode may be set. The length of theGT may be a time region value, for example, k (k≧1) time sample value Tsor one or more OFDM symbols. In the case where RN backhaul downlinksubframes are continuously set or according to a predetermined subframealignment relationship, the GT of a last part of the subframe may not bedefined or set. Such a GT may be defined only in a frequency regionwhich is set for backhaul downlink subframe transmission, in order tomaintain backward compatibility (if the GT is set in an access downlinkinterval, a legacy UE is not supported). In a backhaul downlinkreception interval excluding the GT, the RN may receive a PDCCH and aPDSCH dedicated to the RN from the eNB, which may be expressed byR-PDCCH (Relay-PDCCH) and R-PDSCH (Relay-PDSCH) because they arephysical channels dedicated to the RN.

The RN may be roughly divided into an in-band RN and an out-band RN asdescribed above. In the in-band RN, a Un interface and a Uu interfaceuse the same frequency. In this case, it is necessary to allocatededicated subframes respectively used by the interfaces such thattransmission/reception of the Un interface and transmission/reception ofthe Uu interface do not cause interference with each other. Hereinafter,an uplink/downlink subframe allocated for enabling the RN to communicatewith the DeNB is referred to as an “RN subframe.” That is, the RNperforms data transmission/reception through the Un interface using theRN subframe and performs data transmission/reception through the Uuinterface using the remaining subframe excluding the RN subframe.

Since the RN is wirelessly connected to the DeNB through the Uninterface, a problem (e.g., an out-of-sync problem, radio link failure,etc.) may occur in a radio channel of the Un interface as in the Uuinterface.

If a radio channel problem occurs in the Un interface, a problem mayoccur in data transmission/reception of all UEs under the control of theRN. Accordingly, the RN attempts to preferentially recover the Uninterface.

However, in an in-band RN, data transmission/reception between the UEand the RN causes interference in recovery of connection between the RNand the DeNB. Accordingly, data transmission/reception to/from the UEmust be reduced upon recovery of the connection between the RN and theDeNB and recovery of the connection between the RN and the DeNB must beperformed using the RN subframe.

However, it is not decided how long the RN maintains the Uu interfaceand when the recovery of the Un interface is performed using the RNsubframe. If the Uu interface is continuously maintained when a problemoccurs in the Un interface, since the Un interface is recovered usingonly the RN subframe. Thus, the recover of the Un interface is delayed.

In contrast, if the RN subframe is immediately released when a problemoccurs in the Un interface, since the Uu interface must be alsoimmediately released in order to prevent interference, signalingoverhead and time delay occur in order to establish RRC connection witha UE using the Uu interface after the recovery of the Un interface.

Accordingly, the present invention proposes the following method toattempt recovery of the Un interface using the RN subframe at the RNwhile maintaining the Uu interface during a predetermined time when aradio channel problem occurs in the Un interface.

(1) If a radio channel problem occurs in the Un interface, a timer isrunning and, during the running of the timer, the Un interface isrecovered using only the RN subframe while normally maintaining the Uuinterface.

(2) If the recovery of the Un interface is successful before the timerexpires, the Uu interface and the Un interface are normally maintained,but, if the recovery of the Un interface is not successful before thetimer expires, the Uu interface is released, the RN subframe isreleased, and an attempt to connect the Un interface using a certainsubframe is made.

Hereinafter, an operation for operating a timer and recovering aninterface when an out-of-sync problem has occurred in a physical channeland RLF has occurred will be described in detail.

FIG. 6 is a flowchart illustrating the flow of an operation of a relaynode when an out-of-sync problem occurs in a physical channel of a Uninterface.

(1) The RN determines that an out-of-sync problem has occurred in thephysical channel if N310 consecutive out-of-sync indications arereceived from the physical channel of the Un interface (S610).

The RN determines that the out-of-sync problem has occurred in thephysical channel if the quality of the RS periodically received from theDeNB is less than or equal to a threshold as detected in the physicalchannel.

(2) If the out-of-sync problem has occurred in the physical channel, theRN operates the timer T310 (S620). When the out-of-sync problem hasoccurred in the physical channel, the timer is operated as a procedurefor recovering the interface. When the out-of-sync problem has occurredin the physical channel, the timer T310 may be started.

(3) The RN determines whether N310 consecutive in-sync indications arereceived from the physical channel of the Un interface while the timerT310 is running (S630).

The RN determines that the Un interface has been recovered if a messageindicating that a specific number (N310) of consecutive in-syncindications has occurred is received from the physical channel of the Uninterface while the timer T310 is running.

Meanwhile, the RN maintains the Uu interface while the timer T310 isrunning. In addition, the RN transmits and receives data to and from theDeNB using the RN subframe. In addition, the RN performs interfacerecovery through the RN subframe.

(4) If the RN determines that the out-of-sync problem of the radiochannel of the Un interface has been solved if it is determined that theN310 consecutive in-sync indications are received from the physicalchannel before the timer T310 expires in step S630, and performs normaloperation (S670).

(5) It is determined whether the timer T310 has expired (S640).

(6) If the RN does not receive the N310 consecutive in-sync indicationsbefore the timer T310 expires, the Uu interface is released and the RNsubframe is released (S650).

The RN releases the Uu RBs of all UEs of the Uu interface. In addition,the RN stops system information broadcast using the Uu interface.

(7) After the RN subframe is released, the RN performs the RRCconnection re-establishment procedure to the DeNB using a normalsubframe (S660).

Meanwhile, if the out-of-sync problem continues even when the timer T310has expired, the RN determines that RLF has occurred and performs an RRCconnection re-establishment procedure.

If the recovery of the Un interface is not successful before the timerexpires, the RN subframe is released and an attempt to connect the Uninterface using not only the RN subframe but also another subframe, thatis, a normal subframe, is made. That is, the RN performs a random accessprocedure using a normal subframe.

FIG. 7 is a flowchart illustrating the flow of an operation of a relaynode when RLF occurs in a Un interface.

(1) The RN detects RLF of the Un interface (S710).

As described above, RLF occurs in the following three situations.

1) First, it may be determined that RLF has occurred if a specificnumber (N310) of consecutive in-sync indications is not received until apredetermined time elapses after a specific number (N310) of consecutiveout-out-sync indications is received from the physical channel of the Uninterface due to a problem of the physical channel. 2) Second, it may bedetermined that RLF has occurred if a predetermined number(preambleTransMax) of random access procedures is attempted using the Uninterface but is not successful due to a MAC random access problem. 3)Third, it may be determined that RLF has occurred if the AM RLC layer ofthe Un interface retransmits a specific AMD PDU a predetermined numberof times (e.g., maxRetxThreshold) but transmission is not successfullyperformed due to a maximum RLC retransmission problem.

(2) The RN operates the timer T311 (S720).

If RLF occurs, the RN operates the timer T311 and the timer value has avalue equal to or greater than 0. The timer value is received from theDeNB when the RN first accesses the DeNB.

(3) The RN performs an RRC connection re-establishment procedure usingthe RN subframe in the Un interface while the timer T311 is running(S730).

If RLF occurs in the Un interface, the RN performs an RRC connectionre-establishment procedure in order to re-establish connection with theDeNB. At this time, the RN performs RRC connection re-establishmentusing only a specific subframe. The specific subframe may be the RNsubframe.

(4) It is determined whether the RRC connection re-establishmentprocedure is successful (S740).

(5) If the RN successfully performs the RRC connection re-establishmentprocedure before the timer T311 expires, the RN determines that RLF ofthe Un interface is solved and performs normal operation (S780).

(6) It is determined that the timer T311 has expired (S750).

If the timer T311 has not expired, the RRC connection re-establishmentprocedure is repeated.

(7) If the RN does not successfully perform the RRC connectionre-establishment procedure before the timer T311 expires, the Uuinterface is released and the RN subframe is released (S760).

Release the Un interface when the recovery of the Un interface is notsuccessful before the timer expires includes the following process. Thatis, the RN releases the Uu RBs of all UEs and the RN stops systeminformation broadcast over the Uu interface.

(8) The RN transitions to an RRC_IDLE mode and performs the RRCconnection establishment procedure again with respect to the Uninterface using a normal subframe (S770).

The RN determines that RRC connection failure has occurred when thetimer expires and transitions to the RRC_IDLE mode. Thereafter, the RNperforms the RRC connection re-establishment procedure to the DeNB usingnot only the RN subframe but also a normal subframe. When the timer T311expires, 1) the RN releases the RN subframe, 2) the RN transitions tothe RRC_IDLE mode, and 3) the RN stays in an appropriate new cell andperforms a random access procedure for accessing the cell using a normalsubframe.

The RN may minimize interference by controlling the Uu interface or theUn interface.

First, a method of minimizing interference by controlling the Uuinterface of the RN will be described.

The RN transmits a stop message to UEs by dedicated or common signaling.When each UE receives the stop message, each UE may stop all RBs andprocesses. If the RBs are stopped, a PDCP SDU discarding timer may beoperated.

System information may indicate the state of the RN and the state of theRN may include a normal state, a recovery state and an idle state. 1) Ifthe UE determines that the RN state is in the recovery state, all RBsand processes may be stopped. 2) If the UE determines that the RN stateis in the idle state, the UE releases all RBs, transitions to the idlestate, and searches for another cell in order to establish RRCconnection. 3) If the UE determines that the RN state is in the normalstate, the UE resumes all the stopped RBs and processes.

The RN does not allocate a UL grant to the UE. Even when the RN receivesa buffer status report, a scheduling request or a random accesspreamble, the RN does not respond to the request of the UE. That is, theRN does not allocate the UL grant to the UE.

The RN instructs the UE to transition to a discontinuous reception (DRX)state. The RN may instruct the UE to transition from a continuous stateto a long DRX state.

Next, a method of minimizing interference by controlling the Uninterface of the RN will be described.

While RRC connection re-establishment is performed, that is, before thetimer T311 expires, UL transmission is performed using a MBSFN subframe.

While the timer T311 is running, the RN performs UL transmission onlyusing the MBSFN subframe. When the RN performs a random access procedurewhile the timer T311 is running, the RN uses a previously allocatedrandom access (RA) preamble. The RA preamble is previously allocated bythe DeNB so as to be used by the RN in the event of an emergency such asRLF.

If the timer expires, that is, if RRC connection re-establishment fails,the RN may perform UL transmission using a normal subframe, not using aspecific subframe. That is, the RN may perform UL transmission not onlyusing a MBSFN subframe but also using another subframe after the timerT311 has expired.

FIG. 8 is a block diagram of a communication device according to anembodiment of the present invention.

Referring to FIG. 8, the communication device 800 includes a processor810, a memory 820, an RF module 830, a display module 840 and a userinterface module 850.

The communication device 800 is shown for convenience of description andsome modules may be omitted. The communication device 800 may furtherinclude necessary modules. Some modules of the communication device 800may be subdivided. The processor 810 is configured to perform operationaccording to the embodiments of the present invention described withreference to the drawings. More specifically, for the detailed operationof the processor 810, refer to the description of FIGS. 1 to 6.

The memory 820 is connected to the processor 810 and is configured tostore an operating system, an application, program code and data. The RFmodule 830 is connected to the processor 810 and is configured toconvert a baseband signal into a radio signal or convert a radio signalinto a baseband signal. For conversion, the RF module 830 performsanalog conversion, amplification, filtering frequency up-conversion orinverse processes thereof. The display module 840 is connected to theprocessor 810 and is configured to display a variety of information. Thedisplay module 840 may include, but is not limited to, well-knownelements such as a liquid crystal display (LCD), a light emitting diode(LED) and an organic light emitting diode (OLED). The user interfacemodule 850 is connected to the processor 810 and is configured by acombination of well-known user interfaces such as a keypad and atouchscreen.

The aforementioned embodiments are achieved by combination of structuralelements and features of the present invention in a predeterminedmanner. Each of the structural elements or features should be consideredselective unless specified otherwise. Each of the structural elements orfeatures may be carried out without being combined with other structuralelements or features. Also, some structural elements and/or features maybe combined with one another to constitute the embodiments of thepresent invention. The order of operations described in the embodimentsof the present invention may be changed. Some structural elements orfeatures of one embodiment may be included in another embodiment, or maybe replaced with corresponding structural elements or features ofanother embodiment. Moreover, it will be apparent that some claimsreferring to specific claims may be combined with other claims referringto other claims other than the specific claims to constitute theembodiment or new claims may be added by means of amendment after theapplication is filed.

The embodiments of the present invention are disclosed on the basis of adata communication relationship between a base station and a relay node.Specific operations to be conducted by the base station in the presentinvention may also be conducted by an upper node of the base station asnecessary. In other words, it will be obvious to those skilled in theart that various operations for enabling the base station to communicatewith the UE in a network composed of several network nodes including thebase station will be conducted by the base station or other networknodes other than the base station. The term “Base Station” may bereplaced with the term fixed station, Node-B, eNode-B (eNB), or accesspoint as necessary.

In the case of implementing the present invention by hardware, thepresent invention can be implemented with application specificintegrated circuits (ASICs), Digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), a processor, a controller, amicrocontroller, a microprocessor, etc.

If operations or functions of the present invention are implemented byfirmware or software, the present invention can be implemented in theform of a variety of formats, for example, modules, procedures,functions, etc. The software codes may be stored in a memory unit sothat it can be driven by a processor. The memory unit is located insideor outside of the processor, so that it can communicate with theaforementioned processor via a variety of well-known parts.

Although a method for processing a signal at a radio node in a wirelesscommunication system and an apparatus thereof according to the presentinvention is applied to a 3GPP LTE system, the present invention isapplicable to various wireless communication systems in addition to the3GPP LTE system.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method for operating a device relay node in awireless communication system, the method comprising: communicating, bythe relay node, with a base station using a radio resource in a subframeconfigured for the relay node only; detecting, by the relay node, aproblem with a connection between the relay node and the base station bydetecting consecutive out-of-sync indications; starting, by the relaynode, a timer upon detecting the problem with the connection between therelay node and the base station; and releasing, by the relay node, arestriction of using the subframe configured for the relay node only,when the timer expires.
 2. The method of claim 1, wherein the problemwith the connection between the relay node and the base station isassociated with a radio link failure.
 3. The method of claim 1, furthercomprising: communicating, by the relay node, with the base stationusing any subframe when the started timer expires.
 4. The method ofclaim 1, wherein the step of releasing the restriction comprises:releasing a configuration of using the subframe configured for the relaynode only.
 5. The method of claim 1, further comprising: performing, bythe relay node, a recovery of the problem with the connection betweenthe relay node and the base station while the timer is running.
 6. Themethod of claim 5, wherein the timer is stopped when the problem withthe connection between the relay node and the base station is recovered.7. The method of claim 6, wherein the problem with the connectionbetween the relay node and the base station is recovered after detectingconsecutive in-sync indications.
 8. A node in a wireless communicationsystem, the relay node comprising: a timer; and a processor operativelyconnected to the timer and configured to: communicate with a basestation using a radio resource in a subframe configured for the relaynode only, detect a problem with a connection between the relay node andthe base station by detecting consecutive out-of-sync indications, startthe timer upon detecting the problem with the connection between therelay node and the base station, and release a restriction of using thesubframe configured for the relay node only, when the timer expires. 9.The relay node of claim 8, wherein the problem with the connectionbetween the relay node and the base station is associated with a radiolink failure.
 10. The relay node of claim 8, wherein the processor isfurther configured to communicate with the base station using anysubframe when the timer expires.
 11. The relay node of claim 8, whereina configuration of using the subframe configured for the relay node onlyis released when the timer expires.
 12. The relay node of claim 8,wherein the processor is further configured to perform a recovery of theproblem with the connection between the device relay node and the basestation while the timer is running.
 13. The relay node of claim 12,wherein the timer is stopped when the problem with the connectionbetween the relay node and the base station is recovered.
 14. The relaynode of claim 13, wherein the problem with the connection between therelay node and the base station is recovered after detecting consecutivein-sync indications.